Metal complexes each act as a catalyst in a redox reaction (redox catalyst) involving electron transfer such as an oxygenation reaction, an oxidative coupling reaction, a dehydrogenation reaction, a hydrogenation reaction, or an oxide decomposition reaction, and are each used in the production of an organic compound or polymer compound. Further, the metal complexes are used in various uses including additives, modifiers, cells, and sensor materials. It has been known that these metal complexes exhibit excellent catalyst activity as an oxygen-reduction catalyst and hydrogen peroxide decomposition catalyst (see Z. Liu, F. C. Anson, Inorganic Chemistry, 40, 1329 (2001); and M. D. Godbole et al., European Journal of Inorganic Chemistry, 305 (2005)).
However, when any such metal complex as described above is used as a redox catalyst, the thermal stability and chemical stability of the complex are insufficient, so the use of the catalyst upon performance of a reaction in the presence of an acid or under heating involves a problem. Accordingly, an improvement in stability of a metal complex catalyst against the presence of an acid or heating in a reaction to which the catalyst is applied has been aspired.
A method of subjecting a metal complex to a heating treatment has been described in Tatsuhiro Okada, et. al., Journal of Inorganic and Organometallic Polymers, 9, 199, (1999) as a method of improving the stability of the metal complex. However, the reaction activity of such catalyst as described in the document is not enough for the catalyst to be put into practical use, so an additional improvement of the reaction activity has been demanded.
In addition, the following fact has been known particularly about an assembled metal complex out of the metal complexes: when the metal complexes are assembled, a specific reaction space is provided, so the reaction rate of a redox reaction can be increased, or the reaction selectivity can be controlled (see, for example, Susumu Kitagawa, Ryo Kitaura, Shin-ichiro Noro, Angewandte Chemie International Edition, 43, 2334 (2004)).
It is known that, among the metal complexes, those having a transition metal atom as their center metals exhibit excellent reaction activity as a hydrogen peroxide decomposition catalyst or an oxidative coupling reaction catalyst (see Bulletin of Chemical Society of Japan, 68, 1105 (1995); and Angewandte Chemie International Edition, 42, 6008 (2003)).
However, the stability of the metal complex described in Bulletin of Chemical Society of Japan, 68, 1105 (1995) or Angewandte Chemie International Edition, 42, 6008 (2003) is insufficient in stability, having trouble with the use of the catalyst particularly when the reaction is run in the presence of an acid or when the reaction is run under heating. For this, it has been desired to improve the stability of the metal complex catalyst against the presence of an acid or heating in order to use the metal complex as a catalyst.